This invention relates to a developer material coating apparatus for coating a support member such as a plain paper with granular developer material.
There has been recently utilized a color copying machine in which a color image is formed on a support member such as plain paper using granular developer material and a microcapsule sheet. A color image forming process of this type of color copying machine is as follows. A developer sheet is beforehand formed by coating the developer material on the support member such as plain paper, and the microcapsule sheet is exposed through an original to light to form a latent image on the microcapsule sheet. The microcapsule sheet having the latent image thereon and the developer sheet comprising the support member coated with the developer material are fed to a pressure-developing unit while contacted with each other under pressure. In the pressure-developing unit, the microcapsule sheet and the developer sheet are subjected to a pressure-developing process to develop the latent image on the microcapsule sheet into a visible color image on the developer sheet. Thereafter, the developer sheet having the visible color image thereon is fed to a heat-fixing unit to thermally fix the visible color image on the developer sheet. The developer material is formed of, for example, acid clay, binder and so on, and thus the developer sheet may comprise the support member coated with the developer material formed of the acid clay, the binder and so on.
As described above, this type of color copying machine requires a process for coating the developer material on the support member such as plain paper, and thus a coating apparatus therefor. As a coating apparatus, there has been conventionally used a coating apparatus in which the developer material on the support member is charged with triboelectrification and then is electrostatically coated on the support member.
FIG. 1 shows a conventional coating apparatus C for coating the developer material on the support member such as plain paper. This coating apparatus comprises, for example, a support member feeding unit for feeding the support member to a developer material coating region R in which the support member P is electrostatically coated with the developer material S and then discharging the support member coated with the developer material to an outside of the coating apparatus, and a developer material coating unit for triboelectrically charging the developer material and electrostatically supplying the charged developer material to the support member which has been fed to the developer material coating region R.
The developer material coating unit comprises a tank 50 for accommodating the developer material S therein, a rotatable carry roller 52 for carrying the developer material thereon and a rotatable supply roller 51 for triboelectrically charging the developer material in cooperation with the carry roller 52 and supplying the charged developer material to the carry roller 52. The carry roller 52 and the supply roller 51 are accommodated in the tank 50, and the carry roller 52 is grounded as shown in FIG. 1. The carry roller 52 and the supply roller 51 are rotatably contacted with each other at the peripheral surfaces thereof, and the developer material S is triboelectrically negatively charged at the contacted surfaces of the rollers 51 and 52 through friction between the surface of the carry roller 52 and the developer material S. The charged developer material S is attached to the peripheral surface of the carry roller 52 and then is fed to the developer material coating region R where the charged developer material S is electrostatically supplied from the developer material coating unit to the support member feeding unit.
The support member feeding unit comprises a counter electrode roller 53, which is supplied with a positive voltage from a D.C. power source, a pair of guide rollers 55 and 56 provided away from the counter electrode roller 53, a carry belt 54 such as an endless belt suspended among the counter roller 53 and the guide rollers 55 and 56 for feeding the support member to the developer material coating region while carrying the support member P thereon and discharging the support member coated with the developer material (developer sheet) to the outside of the coating apparatus, and a pushing roller 57 for pushing the support member P against the carry belt 54 to closely contact the support member P with the surface of the carry belt 54. As shown in FIG. 1, since the counter electrode roller 53 is supplied with the positive voltage and the carry roller 52 is grounded, an electric field occurs between the carry roller 52 and the counter electrode roller 53. The charged developer material S carried on the carry roller 52 is electrostatically attracted toward the counter electrode roller 53 with the electric field.
The operation of the developer material coating apparatus as shown in FIG. 1 will be described hereunder.
The support member P which is supplied through a sheet inlet (not shown) to the carry belt 54 of the developer material coating apparatus C while closely contacted with the carry belt 54 by the pushing roller 57, and fed to the developer material coating region R by the rotation of the counter roller 53 and the guide rollers 55 and 56. The negatively-charged developer material S on the carry roller 52 is electrostatically attracted toward the counter electrode roller 53 with the electric field. That is, negatively-charged particles of the developer material S are electrostatically attracted (flight) toward the counter electrode roller 53 in the developer material coating region R where the counter roller 53 and the carry roller 52 are most closely confronted to each other, and attach to the support member P to form a developer material layer 58 on the support member P, that is, a developer sheet. Thereafter, the developer sheet (the support member coated with the developer material 58) is discharged to the outside of the coating apparatus C, and is subjected to a pressure development while contacted with a microcapsule sheet under pressure.
In the conventional developer material coating apparatus thus constructed, the charged developer material S attached on the peripheral surface of the carry belt 52 is intactly transferred to the support member P contacted with the carry belt 54. Accordingly, when the developer material S is unevenly attached to the surface of the carry roller 52 due to unevenness of the surface shape of the carry roller 52, aggregation of the particles of the developer material S or the like (for example, when a striped irregularity of the developer material S occurs along the peripheral surface of the carry roller 52 as shown by irregular coating portions 3a to 3d in FIG. 3), the striped irregularity of the developer material S on the carry roller 52 is also intactly transferred to the surface of the support member P, that is, the developer material S is unevenly coated on the support member in a strip pattern. As a result, after the pressure development, a visible image having a striped irregularity in image density is formed on the support member P.